Miniature wide-angle imaging lens

ABSTRACT

A miniature wide-angle imaging lens has a miniaturization ratio, of a total track length from the center of a first surface to a focal plane by an image circle diameter, with a value less than 3.0. The imaging lens includes, starting from an object side of the lens, a first group of at least three optical elements, a second group including an aperture stop and an optical element immediately in front of or behind the aperture stop, and a third group of at least two optical elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/384,900, filed Dec. 20, 2016, entitled“Miniature Wide-Angle Imaging Lens,” currently pending, which claims thebenefit of U.S. Provisional Patent Application No. 62/387,409, filedDec. 23, 2015, entitled “Miniature wide-angle imaging lens,” nowexpired, and U.S. Provisional Patent Application No. 62/298,795, filedFeb. 23, 2016, entitled “Miniature wide-angle imaging lens,” nowexpired, the entire contents of all of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to optical lenses and more particularly tominiature lenses having a wide-angle field of view.

For most applications requiring wide-angle imaging, larger lensconstructions having a miniaturization ratio (i.e., a total track lengthover an image circle diameter) greater than 3.0 are often used. However,for consumer applications, especially with mobile devices, the trend isthat the lens thicknesses are becoming thinner while the sensor sizesare becoming larger. Accordingly, a new kind of wide-angle lenses with aminiaturization ratio less than 3.0 are required.

Previously suggested miniature wide-angle lenses, such as that describedin “Consumer electronic optics: how small can a lens be: the case ofpanomorph lenses” published in “Proc. SPIE 9192, Current Developments inLens Design and Optical Engineering XV, 91920H,” or as in U.S. Pat. No.8,248,715 or U.S. Pat. App. Pub. Nos. 2014/0029115, 2013/0308206,2014/0226222, 2014/0285906, 2015/0253542, 2015/0268446 or 2012/0212839were designed for previous generations of sensors having smaller sizesand larger pixels. These lenses had lower performance requirements,especially regarding image quality and aperture size. For these existinglens constructions, a total of three to six optical elements were enoughto meet the required performances for these sensors. For the existingwide-angle 6-element lenses, a symmetric construction using 3 elementsin front of the stop and 3 elements behind the stop has been used.However, with new larger sensors and smaller pixels, more complexwide-angle lens constructions using six elements with asymmetricconstructions around the stop or using seven or more elements must bedesigned to achieve the required performances.

One of the challenges to achieve good imaging performance over the wholefield of view of a miniature wide-angle lens is the change of relativeillumination from the center to the edge of the field of view. Inwide-angle lenses, the relative illumination is usually maximum in thecenter and drops continuously toward the edge of the field of view. Theconsequence of lower illumination toward the edge is a lower imagequality at the edge due to increased diffraction effects and additionalsensor noise at the edges.

Another challenge to achieve good imaging performance over the wholefield of view of a miniature wide-angle lens is a drop of the modulationtransfer function (MTF) from the center to the edge of the field ofview. In wide-angle lenses, the image MTF is usually maximum in thecenter and drops continuously toward the edge of the field of view. Theconsequence of lower MTF toward the edge is a lower image quality at theedge.

BRIEF SUMMARY OF THE INVENTION

To overcome all the previously mentioned issues, embodiments of thecurrent invention describe miniature wide-angle imaging lenses having aminiaturization ratio (i.e., total track length from the center of thefirst surface to the focal plane over the image circle diameter) havinga value less than 3.0 while maintaining a good balance between imagequality parameters, including MTF, relative illumination, andresolution. The imaging lens construction, in order from the objectspace to the image space, preferably includes a first group of elements,a second group of elements, and a third group of elements.

The first group of elements, preferably including all the elements infront of the second group, has a negative optical power in the paraxialregion and preferably includes at least three optical lenses. Of theseat least three optical lenses, the first lens on the object side isgenerally a negative meniscus lens with a surface on the object side andaccepting light from an opening angle of at least 100° and generallybetween 120° to 280°.

The second group of elements preferably includes an aperture stop and asingle optical lens immediately in front of or behind the aperture stop.The single optical lens of the second group is preferably a positivelens.

The third group of elements preferably includes at least two opticallenses after the second group. Of these at least two optical lenses,there is generally at least one positive element and at least onenegative element. The last lens element on the image side has a surfaceon the image side transmitting light to an opening angle of at least40°.

In an embodiment of the current invention, the miniature optical lenshas six optical elements, split as three, one, and two elementsrespectively for the first, second, and third groups. In anotherembodiment of the current invention, the miniature optical lens hasseven optical elements in it, split as three, one, and three elementsrespectively for the first, second, third groups. In another embodimentof the current invention, the miniature optical lens has eight opticalelements in it, split as four, one, and three elements respectively forthe first, second and third groups.

In some embodiments of the current invention, the targeted resolutioncurve of the miniature wide-angle lens is configured to offset, at leastin part, the drop of relative illumination from the miniature wide-anglelens by increasing the number of pixels imaged in the zone where therelative illumination is lower.

In some other embodiments of the current invention, the targetedresolution curve of the miniature wide-angle lens is configured tooffset, at least in part, the drop of MTF from the miniature wide-anglelens by increasing the number of pixels imaged in the zone where the MTFis lower.

In some other embodiments of the current invention, the targetedresolution curve of the miniature wide-angle lens is configured as theoptimal curve to produce the highest relative illumination and MTFvalues combination and hence produce the optimal image quality for thewhole lens plus camera system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofa preferred embodiment of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustration, there is shown in the drawings an embodiment which ispresently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements andinstrumentalities shown.

In the drawings:

FIG. 1 is a first preferred embodiment of a miniature wide-angle lenswith six total lens elements;

FIG. 2 is a second preferred embodiment of a miniature wide-angle lenswith seven total lens elements;

FIG. 3 is third preferred embodiment of a miniature wide-angle lens witheight total lens elements;

FIG. 4 is an example of a typical relative illumination curve of aminiature wide-angle lens;

FIG. 5 is an example of a typical MTF curve of a miniature wide-anglelens;

FIG. 6 is an example of a targeted resolution curve used to at leastpartially compensate the relative illumination or at least partiallycompensate the MTF according to certain embodiments of the presentinvention; and

FIG. 7 is an example of a targeted resolution curve chosen to producethe highest relative illumination in the whole field of view whilekeeping the highest MTF according to certain embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower”, and“upper” designate directions in the drawings to which reference is made.The words “inwardly” and “outwardly” refer to directions toward and awayfrom, respectively, the geometric center of the device and designatedparts thereof. The terminology includes the above-listed words,derivatives thereof, and words of similar import. Additionally, thewords “a” and “an”, as used in the claims and in the correspondingportions of the specification, mean “at least one.”

FIG. 1 shows a first embodiment of the present invention with an opticallayout for a design having six optical elements in an asymmetricconfiguration around the stop, having four optical elements before thestop and two optical elements after the stop. The lens 100 is comprisedof the three groups 110, 112 and 114. In this embodiment of theminiature wide-angle lens 100, the first group 110 from the object spaceis made of lenses 120, 121 and 122. The first group has a negative totaloptical power. The second group 112 includes an aperture stop 124 and asingle positive lens 123. The second group 112 has positive opticalpower. In this embodiment of the miniature wide-angle lens 100, thethird group 114 has two optical elements 125, 126 and has a negativetotal optical power.

Light entering the miniature lens 100 hits a first surface of element120 from all directions between an upper angle 130 and a lower angle134. In this example embodiment of FIG. 1, a total field of view aroundthe central field 132 of the lens 100 is 180°, but any total field ofview over 100° can be considered as a wide-angle lens according to thepresent invention.

The light then passes through all the elements 120, 121, 122, of thefirst group 110, the single lens 123 and the aperture stop 124 of thesecond group 112, and the elements 125 and 126 of the third group 114 toreach an IR filter and image sensor 127. More specifically, the lightbeam from direction 130 reaches the sensor 127 at position 144, thelight from direction 132 reaches the sensor 127 at position 142, and thelight from direction 134 reaches the sensor 127 at position 140. For allbeams of light 130, 132 and 134, the chief-ray is defined as the middleray of the three rays drawn because it passes through the center of theaperture stop 124. In this example embodiment, the angle of the cone oflight formed by the chief-rays reaching the sensor plane at positions140 and 144 is over 40° to minimize the dimensions of the lens 100. Whenmeasured with respect to the chief-ray reaching the sensor 127 atposition 142, which represents the optical axis of the lens 100, thechief-ray angle of the extreme rays reaching the sensor at position 140or 144 are over 20°.

The lens 100 has a total track length 150, which is a measure from thefirst surface on the object side of lens 120 to the image sensor 127,and forms an image having a diameter 160, which is a distance on thesensor 127 between the position 140 and the position 144 where the lightbeams from the lower and the upper fields 130, 134 reach the sensor 127.The miniaturization ratio is calculated by dividing the total tracklength 150 over the footprint diameter 160 and is less than 3.0 for anyminiature lens according to the present invention and could even be lessthan 2.0 for an extreme miniature lens.

FIG. 2 shows an embodiment of the present invention with an opticallayout for a design having seven optical elements. The lens 200 iscomprised of the three groups 210, 212 and 214. In this embodiment ofthe miniature wide-angle lens 200, the first group 210 from the objectspace is made of lenses 220, 221, and 222. The first group 210 has anegative total optical power. The second group 212 includes the aperturestop 223 and a single positive lens 224. The second group 212 haspositive optical power. In this embodiment of the miniature wide-anglelens 200, the third group 214 has three optical elements 225, 226, 227and has a negative total optical power.

Light entering the miniature lens 200 hits the first surface of element220 from all directions between the upper angle 230 and the lower angle234. In this example embodiment of FIG. 2, the total field of viewaround the central field 232 is 180°, but any total field of view over100° can be considered as a wide-angle lens according to the presentinvention.

The light then passes through all the elements 220, 221, 222 of thefirst group 210, the aperture stop 223 and positive lens 224 of thesecond group 212, and the elements 225, 226 and 227 of the third group214 to reach the IR filter and image sensor 228. More specifically, thelight beam from direction 230 reaches the sensor at position 244, thelight from direction 232 reaches the sensor at position 242, and thelight from direction 234 reaches the sensor at position 240. In thisexample, an angle of the cone of light formed by the chief-rays reachingthe sensor plane at positions 240 and 244 is over 40° to minimize thedimensions of the lens 200. When measured with respect to the chief rayreaching the sensor 228 at position 242, which represents the opticalaxis of the lens 200, the chief-ray angle of the extreme rays is over20°.

The lens 200 has a total track length 250, which is a measure from thefirst surface on the object side of lens 220 to the image sensor 228 andforms an image having a diameter 260, which is the distance on thesensor between the position 240 and the position 244 where the lightbeams from the upper and the lower fields 230, 234 reach the sensor. Theminiaturization ratio is calculated by dividing the total track length250 over the footprint diameter 260 and is less than 3.0 for anyminiature lens according to the present invention, and could even beless than 2.0 for an extreme miniature lens.

FIG. 3 shows an embodiment of the present invention with an opticallayout for a design having eight optical elements. The lens is comprisedof the three groups 310, 312 and 314. In this embodiment of theminiature wide-angle lens, the first group 310 from the object space ismade of lenses 320, 321, 322 and 323. The first group has a negativetotal optical power. The second group 312 includes the aperture stop 324and a single positive lens 325. The second group 312 has positiveoptical power. In this embodiment of the miniature wide-angle lens 300,the third group 314 has three optical elements 326, 327, 328 and has anegative total optical power.

Light entering the miniature lens 300 hit the first surface of element320 from all directions between the upper angle 330 and the lower angle334. In this example embodiment of FIG. 3, the total field of viewaround the central field 332 is 180°, but any total field of view over100° can be considered as a wide-angle lens according to the presentinvention.

The light then passes through all the elements 320, 321, 322, 323 of thefirst group 310, the aperture stop 324 and lens 325 of the second group312, and the elements 326, 327 and 328 of the third group 314 to reachthe IR filter and image sensor 329. More specifically, the light beamfrom direction 330 reaches the sensor 329 at position 344, the lightfrom direction 332 reaches the sensor 329 at position 342, and the lightfrom direction 334 reaches the sensor 329 at position 340. In thisexample, the angle of the cone of light formed by the chief-raysreaching the sensor plane at positions 340 and 344 is over 40° tominimize the dimensions of the lens. When measured with respect to thechief ray reaching the sensor at position 342, which represents theoptical axis of the lens, the chief-ray angle of the extreme rays isover 20°.

The lens has a total track length 350, which is a measure from the firstsurface on the object side of lens 320 to the image sensor 329, andforms an image having a diameter 360 which is a distance on the sensor329 between the position 340 and the position 344 where the light beamsfrom the upper and the lower fields 330, 334 reach the sensor. Theminiaturization ratio is calculated by dividing the total track length250 over the footprint diameter 260 and is less than 3.0 for anyminiature lens according to the present invention and could even be lessthan 2.0 for an extreme miniature lens.

In some embodiments of the present invention, all of the elements insidethe miniature wide-angle lenses are made of plastic materials in part toease the mass-production or lower the costs. In some other embodimentsof the present invention, the miniature wide-angle lens consist of atleast one glass element to improve the optical performances of theminiature wide-angle lens or to increase the rigidity of when the glasselement is the first element.

FIG. 4 shows a typical relative illumination curve 400 for a miniaturewide-angle lens according to embodiments of the present invention. Theexact values of the relative illumination with respect to the field ofview vary between each embodiment of the present invention, but theoverall shape having a value around 100% at 0° shown at center 410 andunder 80% at the maximum field angle shown at position 420 is present inall families of miniature wide-angle lenses according to the presentinvention.

FIG. 5 shows a typical sagittal MTF curve 500 and tangential MTF curve505 for a miniature wide-angle lens according to embodiments of thepresent invention. The exact values of the MTF with respect to the fieldof view vary between each embodiment of the present invention and alsovary according to the spatial frequency at which the MTF is calculated,but the overall shape having a higher value at 0° shown at center 510than at the edge shown at position 520 is present in all families ofminiature wide-angle lenses according to the present invention.

FIG. 6 shows an example targeted resolution curve 600 for a miniaturewide-angle lens according to embodiments of the present invention wherethe targeted resolution is non-linear and a higher number of pixels perdegree is intentionally present in a part of the image. In someembodiments of the miniature wide-angle, the shape of the targetedresolution curve is intentionally designed to compensate for the drop ofrelative illumination seen in FIG. 4. In some other embodiments of theminiature wide-angle lens, the shape of the targeted resolution isintentionally designed to compensate for the drop of MTF seen in FIG. 5.In the zone where the resolution is higher, there are more pixels of thesensors used to image a given angle of the object space. By having moreimaging pixels in this zone, this compensates for the lower imagequality in this zone either due to the lower relative illumination orthe lower MTF. The final resulting image can then be processed to createa resulting image with constant image quality across the whole field ofview.

FIG. 7 shows another example embodiment of a non-linear targetedresolution curve 700 for a miniature wide-angle lens according to thepresent invention. The targeted resolution curve is chosen to have anupward curve between the center resolution value 710 and a maximum 712(number of pixels/degree), followed by a downward curve between themaximum 712 and a region near the edge of the field of view aroundposition 714. This downward curve between maximum value 712 and position714 allows the lens system to have a higher relative illumination valuetoward the edge of the field of view by having a lower object to imagemagnification ratio in that region and hence redirecting the samequantity of light from an object to a smaller region in the image withmore illumination.

In some embodiments of a miniature wide-angle lens according to thepresent invention, the resolution curve has a change of direction at theedge of the field of view 716. This change of direction is an upwardtrend if it is preceded by a downward trend and it is a downward trendif it is preceded by an upward trend. This change of direction allowsfor a closer value of resolution in pixels/degree in the center 710 andat the edge 716, creating the best balance of MTF between the center 710and the edge 716.

Combined together, the downward curve between maximum value 712 andposition 714 allowing higher relative illumination and the change ofdirection in the curve between position 714 and edge provides 716 thebest image quality on the lens and camera system. The more balancedrelative illumination creates less sensor noise in the images due doillumination differences and less difference of diffraction effects onthe image quality due to the variable f/# across the field of view. Forthe more balanced MTF, thanks to the change of direction betweenposition 614 and edge 616, it is directly related to the image qualityof the lens.

All of the above are figures and examples of miniatures wide-anglelenses. They are examples of families of constructions having threegroups and at least six optical elements. Furthermore, the miniaturewide-angle lenses can be optimized according to a function which atleast includes the relative illumination, the resolution and the MTF.Similar constructions are possible and the three examples presentedshould not limit the scope and spirit of the present invention. It willbe appreciated by those skilled in the art that changes could be made tothe embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. A miniature wide-angle optical apparatuscomprising: a light-receiving first surface; a focal plane; a totaltrack length measured from a center of the first surface to the focalplane; a miniaturization ratio with a value less than 3.0, theminiaturization ratio being a ratio of the total track length divided byan image circle diameter; and a non-linear targeted resolution tointentionally create a zone in an image captured by the miniaturewide-angle optical apparatus with a lower object to image magnificationcompared to linear targeted resolution, the lower object to imagemagnification being used to compensate, at least in part, for a lowerimage quality due to at least one of a drop of relative illumination ora drop of MTF in a zone of the image.
 2. The miniature wide-angleoptical apparatus of claim 1, wherein the optical apparatus isconfigured to create a resulting image with a constant image qualityacross a whole field of view.
 3. The miniature wide-angle opticalapparatus of claim 1, wherein a targeted resolution curve has a changeof direction near an edge of a field of view.
 4. The miniaturewide-angle optical apparatus of claim 1, wherein an opening angle oflight entering the optical apparatus is over 100°.
 5. The miniaturewide-angle optical apparatus of claim 1, wherein an angle of chief-raysreaching the focal plane is over 20° from an optical axis of the opticalapparatus.
 6. The miniature wide-angle optical apparatus of claim 1,further comprising a plurality of optical elements, at least one of theplurality of optical elements defining the first surface.
 7. Theminiature wide-angle optical apparatus of claim 6, wherein at least oneof the optical elements is made of glass.
 8. The miniature wide-angleoptical apparatus of claim 1, wherein the miniaturization ratio value isless than 2.0.